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Hi 

I'm operating a 912iS Sport with an MGL iEFIS. I found a-5-6% difference between the Hobbs counter in the MGL system (That is supposed to show engine operating hours) and the time measured by the ECU seen when connecting the BUDS SW.

any ideas as why is this difference.

  • Re: Operating Hours monitoring

    by » 2 weeks ago


    Yes, the latest firmware update for G3 IEFIS contains this: "Fixed a small issue related to using RDAC units for 91xiS and ULP engines. With engine ECU off the RDAC sends a RPM of 9001 as easily visible indication. In order to prevent this from triggering hobbs this RPM is ignored but only in case a certain messsage is received on the CAN bus from the RDAC that is only sent by these RDAC versions. This is sent every 4 seconds but the timeout was set to 3 seconds. This could, depending on message timing result in the hobbs counting at about 1/4 rate. It however works correctly with ECU communicating."


  • Re: Operating Hours monitoring

    by » 2 weeks ago


    I have just installed the latest G3 version and hope it will solve this issue. But, if I understand your desciption correctly, I have a differant problem. The ECU operating hours counter shows a higher number of hours than the EFIS conter.

    Can you explane it?


  • Re: Operating Hours monitoring

    by » 2 weeks ago


    I have the same issue and I’ve got a Dynon system.  Nobody has been able to explain what ENGINE time means - nobody on this forum, VAF, nor the experts at Lockwood.  I started a thread on this subject a couple of months ago.  Out of the box mine showed 0.5 hours but now that I’ve got over 130 hours on the Hobbs, ENGINE time is now 0.6 hours BEHIND Hobbs.  I’m probably going to remove it from my EMS screen since it appears to have no value.

    Purely a guess on my part, but it seems to more closely correlate to the time the engine spends above the 120 degree oil temperature, but this is merely a guess on my part.  If you learn the answer from an authoritative source, please share.  Inquiring minds want to know.


  • Re: Operating Hours monitoring

    by » 2 weeks ago


    Don't worry about engine time. Use your Hobbs time for your maint. time and other needs.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Operating Hours monitoring

    by » 2 weeks ago


    With advanced avionics comes more bells and whistles than you may know what to do with.
    Timers are a nearly free addition to the instrumentation so the designer throws extra in to make the marketing guys happy.

    Hobbs: The old tried and true clock that runs whenever the engine does.

    Tach: Think of it as an odometer for the engine.  The faster the engine runs the more "Hours" the Tach Meter accumulates.
    If 5500 RPM is considered to be full continuous power, then the Tach meter will accumulate an "Hour " for every actual clock hour.
    At 2750 RPMs it will take 2 clock hours to accumulate 1 Tach "Hour".
    It is really counting Engine Revolutions and then displaying another minute for every 5500 revolutions no matter how long it actually takes to go around that many revs.  
    This gave the military mechanics a break on the engine rebuilds when the pilots spent hours idling while waiting to launch a mission.

    Rotax does NOT use Tach hour for any record-keeping. It is Hobbs time Only!

    Engine: This is just another Hobbs Timer that can be used to record Engine Hours Separate from Airframe hours.
    In a new aircraft with a new Engine, the Hobbs and Engine hours will be the same.
    Technically, the new engine arrived with an hour or so of factory test time on it so they should be close but not exactly the same.
    Many people just ignore this small difference.
    After an overhaul, the engine hours will be reset back to Zero while the Hobbs hours continue ticking.
    If you eventually replace an engine, the Hobbs Hours will be way more than the Engine hours.
    If you initially installed a used engine in your new airframe the Engine hours will be way more than the Hobbs.

    Before the advent of electronic EFIS systems, all these hour differences were recorded as paper entries in the Logbooks, and still should be.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


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